Hot-wire measurement technology is used to determine fluctuation variables and flow turbulence in wind tunnels and to analyse unsteady flow structures on compressors.
The Engine Acoustics Department uses hot-wire measurement technology to analyse the degree of turbulence in wind tunnel flows and to investigate unsteady flow structures on high-speed compressors. The changing variables are measured and the flow turbulence is determined. The periodic changes in velocity and the characteristics of the flow turbulence have a direct influence on the efficiency and noise generation of an engine or flow body in the wind tunnel.
DLR's hot-wire measurement system is based on constant temperature anemometry (CTA) and uses the cooling effect of a flow on a heated thin sensor wire. Very thin wires with a diameter of 9-12.5 µm are electrically heated and cooled by a passing fluid. This cooling effect can be measured via a voltage change and then converted into a velocity with high frequency resolution. In this way, transient flow effects can be measured and visualised over a wide range. X-wire probes are used to measure the axial and lateral flow components.
The data generated in this way can be used as boundary conditions for numerical analyses. The high-resolution time series can be used to determine the degree of turbulence, the integral turbulent length and the turbulent kinetic energy, which are important input boundary conditions for CFD simulations and their turbulence models.
